1. Field of the Invention
The present invention relates to an apparatus, a method, and a computer-readable recording medium for map creation.
2. Description of the Related Art
Conventionally in an automotive navigation system of providing a routing assistance at the current location and to a destination in car driving, a self-position of a car is basically identified based on positional information from the GPS (Global Positioning System) satellite. Since there is a difficulty in receiving electric waves of the GPS in an inside of a tunnel, in a space sandwiched by high-rise buildings, under an elevated road, in a wooded area, and the like due to a strong rectilinear property of the electric waves and errors may arise only by the GPS, the self-position of the car is identified by using, in combination with the GPS, a stand-alone navigation based on information of an acceleration sensor and a gyroscope in the automotive navigation system, car speed signals associated with the rotation of tires, and the like.
Besides, since errors may arise due to a condition of a road surface and tires in a stand-alone navigation, a method of applying the self-position to road data on a map with software technique called “map matching” to compensate for errors by the GPS, the gyroscopic sensor, and the like has been used.
In addition, as a technique of using a laser range sensor, a camera, an encoder, and the like to grasp the self-position to an accuracy of several to several tens of centimeters, an SLAM (Simultaneous Localization And Mapping), which is a technique of performing an estimation of self-position and a creation of an environmental map at the same time, has been known. Especially, an SLAM using a camera is called “Visual SLAM”. It is possible in the Visual SLAM technique, since a local map is created by the sensor and the self-position of the car is identified from map information, to identify the self-position of the car accurately even in the situation with the difficulty in the reception of electric waves of the GPS. Moreover, since the Visual SLAM technique uses external information, which is different from the gyroscopic sensor and the acceleration sensor, it is possible to identify the self-position of the car regardless of conditions of a road surface and tires.
Japanese Laid-open Patent Publication No. 2014-095553 discloses a camera posture estimation apparatus capable of improving an accuracy of estimating a rotation angle (camera posture) indicating a position and an attitude, with respect to a subject, of a camera that captures an image of the subject by using the Visual SLAM technique. Since in estimating a three-dimensional position of an area corresponding to a template image, estimating the three-dimensional position of the template image after eliminating outliers from feature point included in the area, the camera posture estimation apparatus disclosed in Japanese Laid-open Patent Publication No. 2014-095553 is capable of improving an accuracy of the three-dimensional position by suppressing an affect by outliers.
To drive a car while identifying the self-position of the car by using the Visual SLAM technique, it is necessary to initialize a map used for an estimation of an initial self-position. It is required in this map not to include three dimensional point information of moving objects such as a human being and a car since the map requires only three dimensional point information of a motionless object such as a building, a road, and a traffic sign.
However, in the camera posture estimation apparatus disclosed in Japanese Laid-open Patent Publication No. 2014-095553, there is a problem that the map cannot be initialized at an arbitrary timing irrespective of the presence of moving objects such as a human being and a car in creating, in advance, a map not including three dimensional point information of moving objects.
Therefore, there is a need for an apparatus, a method, and a computer-readable recording medium for map creation, capable of creating an initial map which is applicable to an estimation of self-position.